These experiments are to record firing patterns of neurons in the pontomedullary reticular formation (PMRF)which project into the ipsilateral ascending medial longitudinal fasciculus (MLF) during eye movements in alert cats. A most pressing oculomotor problem is to relate the anatomical connectivity of neurons with their behavioral firing patterns in order to explain neurological deficits. Tremendous progress has been made through recording of eye-movement-related PMRF neurons. The tight coupling of neuronal firing to eye movements implies that these neurons are almost certainly in the immediate supramotoneuronal control circuits. PMRF output and input connections are being investigated by anatomists and electrophysiologists. Some PMRF neurons project into the ipsilateral ascending medial longitudinal fasciculus (MLF) to terminate in various brainstem structures involved in eye movements. These experiments go further than previous ones by both determining the anatomical projection and the behavior of single neurons simultaneously. In this way, the PMFRF's output signals to the MLF will be behaviorly defined. Firing patterns will be quantitatively related to eye and passive head movements and statistically analyzed. Eye-movement deficits due to MLF lesions (internuclear ophthalmoplegia) and PMRF lesions will thereby be better explained. A better anatomico-physiological explanation for eye-movement deficits caused by vascular accidents, multiple sclerosis, tumors, brainstem injuries, congenital nystagmus, the Arnold-Chiari malformation, schizophrenia and certain other conditions should result.